Electrodeposition of ruthenium

ABSTRACT

THICK ELECTRODEPOSITS OF RUTHENIUM CAN BE OBTAINED BY ADDING AN ELEMENT SELECTED FROM GALLIUM, INDIUM, AND THALLIUM IN A STABLE AND SOLUBLE FORM. THE DEPOSITS OBTAINED ARE PRIMARILY CHARACTERIZED BY THEIR LOW STRESS AND ABSENCE OF SURFACE CRACKS AT THICKNESS UP TO ABOUT 10 MILLIMICRONS.

United States Patent @fice 3,630,856 ELECTRODEPOSITION OF RUTHENIUMAndre Meyer, Geneva, Switzerland, assignor to Sel-Rex Corporation,Nutley, NJ.

No Drawing. Filed Mar. 20, 1970, Ser. No. 21,533 Claims priority,application Switzerland, Mar. 21, 1969, 4,277 69 Int. Cl. C23b /32 US.Cl. 204-43 2 Claims ABSTRACT OF THE DISCLOSURE Thick electrodeposits ofruthenium can be obtained by adding an element selected from gallium,indium, and thallium in a stable and soluble form. The deposits obtainedare primarily characterized by their low stress and absence of surfacecracks at thicknesses up to about millimicrons.

The present invention relates to a method for the electrodeposition ofruthenium and to an aqueous bath for carrying out this method.

It is known to electrolytically produce ruthenium coatings by using, asan electrolyte, a complex having the formula (NH [Ru Cl (H O') N],containing 34.4% in Weight of ruthenium metal, at several currentdensities.

The ruthenium coatings so obtained are characterized by severe innerstress, so that they show cracks when their thickness is above 1.0 to1.5 m. Today most commercial applications of parts plated with rutheniumrequire substantially thicker coatings, usually of the order of aminimum thickness of 2.5 ,um. to 5 ,um. or even, on occasion, somewhatthicker, up to about 10 m.

The object of the present invention is to permit the electrodepositionof ruthenium coatings of a thickness sufficient to meet contemporaryindustrial needs. In particular, it is an object of the presentinvention to permit the production of ruthenium coatings of a thicknessof up to about 10 ,um. while comprising no visible cracks even at amagnification of 500 times.

This invention is based on the discovery that the addition of one of theelements selected from gallium, indium and thallium in the form of astable, soluble compound to a ruthenium plating solution, serves toseverely reduce inner surface stress of the plated ruthenium to thepoint where relatively thick deposits of ruthenium electroplate can beobtained. In general, one of the elements selected from gallium, indiumand thallium is added in concentration from 50 mg./l. up to saturationto an aqueous solution of a ruthenium compound which contains from about0.5 g./l. to about 50 g./l. of ruthenium metal.

The addition of at least one metal selected from gallium, indium andthallium, as stable and water soluble compounds, results in coatingswhich are more ductile. These metallic compounds which appear in thecathodic film during the electrolysis modify the cathodic polarizationand the crystallization phenomena, and produce coatings which arecompletely dilferent from those heretofore obtained by known methods, intheir appearance (brighter and clearer), in their mechanicalcharacteristics (more ductile, without cracks), and in theircomposition, the metals of addition being co-deposited with theruthenium during the electrolysis. Some secondary eflfects due to theaddition of these metals have also been found, especially a slightimprovement of the cathodic elficiency, almost at high current density,and a higher power of macro and micro-repartition.

3,630,856 Patented Dec. 28, 1971 EXAMPLES (1) A bath has been preparedcontaining:

Ruthenium: 10 g./l. as a complex of containing 34.4% in weight ofruthenium metal Indium: 5 g./l. (as sulfate) Ammonium sulfamate: 15g./l. (conductivity salt) pH adjusted to 1.5 by means of NH OH or HCl orH 80 Temperature of the bath: 60 C. Current density: 1 amp.dm.

The light coatings, produced on samples of brass precoated with a flashof gold, showing no visible cracks or micro-cracks, to thicknesses up toabout 10 ,uI'IL, have been obtained at a plating rate of 12mg./amp.min., that represent 1 ,um. in 9 minutes. These depositscontained about 1.2 to 1.5% indium.

(2) Deposits have been effected by means of the following bath:

Ruthenium: 10 -g./l. as a complex of Indium: 3 g./l. (as sulfamate)Ammonium sulfamate: 5 g./l.

Sulphamic acid: 5 g./l.

Sulfuric acid up to a pH of 1.0 to 1.5

Temperature of bath: 65 to C.

Current density: 1 amp.dm.

Bright coatings of ruthenium were obtained on brass samples precoatedwith a flash of gold which showed no visible cracks or micro-cracks, andfor this thicknesses up to 10 ,um. These coatings were obtained at aplating rate of 11 m-g./amp.min. These deposits contained about 1.0 to1.3% indium.

Along with the deposit of ruthenium there will be a codeposit of theGroup III-B metal chosen. That codeposit will generally be on the orderof about 0.1% to 10.0% of the total content of the electrodeposit. Atabout 5 g./l. of a Group III-B metal, the metal will codeposit withruthenium in a range of about 1.0 to 2.0%.

The above examples have only an illustrative purpose and are not to beconsidered, in any way, as being limitative.

Experience has shown that indium and gallium give the best result,thallium being less soluble and presenting a tendency to crystallizepartially.

The effects of the addition are substantial from a concentration ofabout 100 mg./l. the maximum eifect being obtained, however, with anaddition of 5 g./l. of indium, for instance. Above this concentration,no substantial supplementary effect appears.

At pH higher than 1.5, the deposits obtained are less bright and have agreater tendency to present micro-cracks and pits which alter itsappearance.

The cathodic efliciency increases with the temperature. Between 6.0 andit is practically constant. On the other hand, it shows a tendency todecrease while the current density increases.

The plating can be effected on any support permitting anelectrodeposition, especially on the same supports as those which permitthe coating of gold, like brass, nickel, titanium, etc.

So as to produce a better adherence and for limiting the formation ofporous deposits, it is advantageous, in some cases, to apply on thesupport, before the electrodeposition of ruthenium, a flash of gold.

I claim:

1. A method for electrodepositing ruthenium by passing a current throughan aqueous solution containing from about 0.5 g./l. to about 50 g./L ofruthenium and at least one element selected from the group consisting ofgallium, indium and thallium in a stable and soluble form and in aconcentration from about 50 mg./l. up to saturation, whereby rutheniumis deposited on the cathode.

2. An aqueous electroplating solution containing from about 0.5 g./1. toabout 50 g./l. of ruthenium and at least one element selected from thegroup consisting of gallium,

References Cited Frederick A. Lowenheim: Modern Electroplating, p. 6,1968.

GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 75172; 20447

